1. Field of the Invention
This invention relates to character recognition systems, and particularly to a system employing a single gap magnetic sensing head for reading characters of the so called E-13B character font, the characters typically being formed on paper by an ink containing magnetic particles. The print specifications appear in ANSI X3.2-1970, published by American National Standards Institute, Inc.
2. General Description of the Prior Art
In single gap character reading systems, a single analog input waveform is obtained by passing the character to be sensed beneath a magnetic transducer having a single flux gap. The signal generated by this head is a derivative waveform representing the rate of change of magnetic flux linking the head as the characters are scanned. Since the distribution of ink, and thus flux, associated with each different character is unique, the waveform derived for each different character uniquely identifies that character.
A variety of systems have been proposed in the past, and they generally fall into two main groups--those using waveform correlation techniques, and those employing pulse, hybrid and miscellaneous techniques. With respect to the latter group, they may be further categorized in terms of their use of binary, ternary, multi-level (more than ternary), and other generally more complex waveform classifications. The present invention employs a ternary form of classification, and U.S. Pat. Nos. 3,363,756, 3,541,508, and 3,571,793 are particular examples of systems using this classification. Additionally, U.S. Pat. No. 3,818,446, although basically a binary type, is of interest.
Quite significantly, a number of the patents recognize the problem of accurately identifying the position of detected signals in terms of their recorded position on recorded media. To overcome this problem, the correlation type systems generally rely on maintaining a rather critical stability of delay lines, and the pulse type systems depend heavily for their accuracy on the rate and commencement of decoding pulses from a pulse generator which must be extremely accurately timed. Heretofore this timing has generally depended upon the derivation of a reference time from a character to be decoded, and, unfortunately, this requires that the speed of movement of the document containing the character and pulse rate be maintained with very close limits, which is difficult and expensive. Accordingly, for the reasons cited, and others, existing character reading systems are generally complex and expensive.
It is an object of the present invention to overcome the aforementioned and other problems present with existing character recognition systems, and particularly to provide an improved system wherein the system tolerances are significantly relaxed, enabling required accuracy to be achieved at a reduced cost.